Estimation of Leaf Photosynthetic Capacity From Leaf Chlorophyll Content and Leaf Age in a Subtropical Evergreen Coniferous Plantation

Abstract Photosynthetic rate is a key source of uncertainty in the modeling of the terrestrial carbon cycle. Recent studies have utilized leaf chlorophyll content (Chl) as a proxy for leaf photosynthetic capacity in croplands and deciduous forests, with little investigation into this relationship for other plant function types and for different leaf ages. In this study, we evaluated the relationship between the maximum rate of carboxylation (V cmax25 ) and the maximum electron transport capacity (J cmax25 ) at 25 °C with both leaf nitrogen and Chl from different leaf ages (current and previous year) in Masson's pine ( Pinus massoniana Lamb.) and slash pine ( Pinus elliottii Engelm.) species in a subtropical evergreen coniferous forest. Our results showed small changes in leaf nitrogen over the growing season. In contrast, V cmax25 , J max25 , and Chl displayed larger seasonal variations. V cmax25 was more related to leaf Chl than leaf nitrogen in both previous year's and current year's leaves, likely due to the variable partitioning of leaf nitrogen between and within photosynthetic and nonphotosynthetic fractions. Leaf Chl and month after budding (MAB) were the main predictors for V cmax25 based on the random forest regression analysis. These findings highlighted the problem in using leaf nitrogen as a proxy for V cmax25 where there is a dynamic nitrogen investment (i.e., with leaf ontogenesis, or between different species) and illustrated the value of using leaf Chl (as retrievable from remotely sensing) and MAB to constrain V cmax25 in process‐based models to improve the simulation of photosynthetic rates in evergreen coniferous forests.